In particle beam cancer therapy systems, an injector is used as a pre-stage accelerator for injecting a particle beam into a circular accelerator. A linear accelerator is used as the injector in many cases. In ion beams, interaction (electric repulsive force) between individual particles (ions) in the ion beams is referred to as space-charge effect. Since the repulsive force is mitigated with increasing energy, acceleration is required as much as possible in the pre-stage of injection into the circular accelerator.
As for protons, for example, it has been known that a linear accelerator suitable for accelerating a beam from an ion source and a linear accelerator manufacturable in a relatively compact size as two stage acceleration are different in structure. In applications other than particle beam cancer therapy systems, connecting of multiple-type linear accelerators in series has been also employed for acceleration up to a relatively high energy level.
Ordinarily, in a case of supplying radio frequency waves to an accelerator (a radio frequency accelerator) having two radio frequency cavities, the radio frequency waves supplied to each radio frequency cavity need to be synchronized with respect to the beam. For that reason, it is necessary to input the radio frequency waves having the same frequency and synchronized phases into each radio frequency cavity. Furthermore, the radio frequency power input into each radio frequency cavity and the respective phases of the radio frequency waves input into the two radio frequency cavities are designed and adjusted for the beam to have good quality and high transmission efficiency (see Patent Document 1 for example).
A radio frequency wave of high power needs to be supplied to the radio frequency accelerator. High-power radio frequency generators are expensive and made using vacuum tubes in many cases. This involves replacement of the tubes, raising a problem of increasing maintenance costs. For that reason, using a power distributor for supplying power to the two radio frequency cavities brings about merits of low costs and reliability improvement because of reduction in the amount of power generators (see Patent Document 2 for example).
However, generation of the high radio frequency power by one power generator and distribution of the radio frequency power by a resonant-coupler-type power distributor cannot adjust independently the respective phases of the radio frequency power to be supplied to the cavities because of a problem due to the principle of the power distributor. Moreover, it has been relatively difficult to adjust the power to each cavity for the beam to have good quality and high transmission efficiency.